https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67104
Bug ID: 67104
Summary: Constant expression factory function initializes
std::array with static storage duration strangely
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: moritz at klammler dot eu
Target Milestone: ---
Created attachment 36110
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36110&action=edit
Source code to reproduce the problem
The following program -- that, to my best knowledge, is valid C++14 -- if
compiled with GCC fails at the marked assertion. If compiled with Clang, both
assertions hold.
#include <array>
#include <cassert>
namespace /* anonymous */
{
constexpr auto
make_array(const int val) noexcept
{
std::array<int, 2> result = { { val, 0 } };
return result;
}
// Replacing `constexpr` by `const` doesn't change anything.
constexpr auto numbers_static = make_array(42);
}
int
main()
{
const auto numbers_automatic = make_array(42);
assert(numbers_automatic[0] == 42); // okay
assert(numbers_static[0] == 42); // fails
}
Attached are the source code, preprocessor output and standard error output
when compiling with GCC 5.1.0 using this command:
$ g++ -std=c++14 -v -save-temps -Wall -Wextra -Werror -pedantic main.cxx
There are no warnings or errors reported by the compiler.
This issue has already been discussed on Stack Overflow where I have posted a
more complicated example to trigger the behavior.
https://stackoverflow.com/questions/31762429/initializing-stdarray-with-static-storage-duration-with-a-parameter-pack-expan
The reduced example included in this report is courtesy of Stack Overflow user
Columbo who has also tried different versions of GCC that reproduced the
behavior.
